1. Field of the Invention
The present invention relates to a failure prediction apparatus and a failure prediction method for performing failure prediction for a laser diode employed in an optical transmission apparatus.
2. Description of the Related Art
In a related art optical transmission apparatus, an optical signal is amplified with laser light generated by oscillation in a laser diode, and the optical level of the optical signal is kept constant. The optical level of the optical signal is always monitored in the optical transmission apparatus. Then, if the optical level is not constant, the value of the current that flows through the laser diode is adjusted so that the optical level is kept constant.
In general, the value of a current necessary to maintain a constant optical level of the optical signal varies depending on the environment around the laser diode, its degradation, and the like. A change in the current value is successively outputted on a monitor in such an optical transmission apparatus. A maintenance person predicts a time point for changing the laser diode or a time point for switching to a reserve system on the basis of comparison between an empirically determined threshold value for the current and the value of the current that flows through the laser diode.
Further, a technique is disclosed in which a child station in an optical transmission apparatus detects a change in the current flowing through a laser diode. The child station then modulates the change component of the current as a part of an optical signal, and transmits the signal to a parent station in the optical transmission apparatus. The parent station monitors degradation and the like in the laser diode (see Japanese Laid-Open Patent Publication No. 58-75336).
Further, a technique is disclosed in which a maintenance person can check equipment at a field site where the equipment is installed using an equipment diagnosis system, even though the equipment is off line. In this technique, the life expectancy of equipment is predicted on the basis of acquired inspection data and a relational formula for estimating the life expectancy of the equipment (see Japanese Laid-Open Patent Publication No. H7-55868).
Nevertheless, the related art optical transmission apparatus has a problem in that a failure time point due to degradation in the laser diode cannot be predicted automatically and accurately. That is, since a maintenance person predicts a failure time point of the laser diode on the basis of a comparison between an empirically determined threshold value for the current and the value of the current that flows through the laser diode, a failure time point of the laser diode in the optical transmission apparatus cannot be predicted automatically if the specification of the failure time point does not have sufficient accuracy.
Further, normal optical transmission cannot be performed in the optical transmission apparatus when degradation in the laser diode progresses more rapidly than expected for any reason. When degradation in the laser diode progresses more rapidly than expected, a failure occurs in the laser diode at a time point earlier than a failure time point empirically predicted by a maintenance person. This causes a serious problem to society.
Further, according to the technique disclosed in Japanese Laid-Open Patent Publication No. S58-75336 described above, the parent station in the optical transmission apparatus can monitor a change in the current that flows through the laser diode, but cannot automatically predict a failure time point of the laser diode.
Further, according to the technique disclosed in Japanese Laid-Open Patent Publication No. H7-55868 described above, the equipment diagnosis system can predict the life expectancy of the equipment. Nevertheless, this prediction of the life expectancy is performed merely in order to obtain an in-the-field temporary diagnosis concerning the availability of operation and the like, and hence an accurate life expectancy cannot be estimated.